Quantum field theory in de Sitter and quasi-de Sitter spacetimes: Revisited

Understand

It is possible to associate temperatures with the non-extremal horizons of a large class of spherically symmetric spacetimes using periodicity in the Euclidean sector and this procedure works for the de Sitter spacetime as well.

• But, unlike e.g., the black hole spacetimes, the de Sitter spacetime also allows a description in Friedmann coordinates.
• This raises the question of whether the thermality of the de Sitter horizon can be obtained, working entirely in the Friedmann coordinates, without reference to the static coordinates or using the symmetries of de Sitter spacetime.
• We discuss several aspects of this issue for de Sitter and approximately de Sitter spacetimes, in the Friedmann coordinates (with a time-dependent background and the associated ambiguities in defining the vacuum states).